Preheat oven to 450 degrees. Coat a shallow roasting pan with nonstick spray.
Combine bread crumbs, crushed onions, Parmesan, sage, the 1/2 tsp. salt, and the 1/4 tsp. pepper in a bowl, then spread on a baking sheet.
Smear mustard all over pork. Roll pork in seasoned crumbs, then place in the prepared roasting pan.
Arrange onion, peppers, sweet potato, cauliflower, and broccoli around roast. Drizzle vegetables with oil; season with salt and pepper.
Roast meat and vegetables at 450 degrees until pork begins to brown, about 10 minutes. Reduce temperature to 275 degrees, but do not remove pan from the oven. Roast pork until it reaches an internal temperature of 155 degrees fro medium, about 90 minutes.
Remove pan from oven; cover roast with foil and let meat rest for 10 minutes. Makes 8 servings.